/**
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.elasticsearch.common.inject.internal;

import com.google.common.base.Function;
import com.google.common.collect.MapMaker;

import java.util.Map;

/**
 * Lazily creates (and caches) values for keys. If creating the value fails (with errors), an
 * exception is thrown on retrieval.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public abstract class FailableCache<K, V> {

    private final Map<K, Object> delegate = new MapMaker().makeComputingMap(
            new Function<K, Object>() {
                public Object apply(@Nullable K key) {
                    Errors errors = new Errors();
                    V result = null;
                    try {
                        result = FailableCache.this.create(key, errors);
                    } catch (ErrorsException e) {
                        errors.merge(e.getErrors());
                    }
                    return errors.hasErrors() ? errors : result;
                }
            });

    protected abstract V create(K key, Errors errors) throws ErrorsException;

    public V get(K key, Errors errors) throws ErrorsException {
        Object resultOrError = delegate.get(key);
        if (resultOrError instanceof Errors) {
            errors.merge((Errors) resultOrError);
            throw errors.toException();
        } else {
            @SuppressWarnings("unchecked") // create returned a non-error result, so this is safe
                    V result = (V) resultOrError;
            return result;
        }
    }
}
